1. Field of the Invention
This invention relates to improvements in a method of plate rolling with a plate mill and an equipment therefor, and particularly to a method of plate rolling of plan view pattern control and an equipment therefor.
2. Description of the Prior Art
In general, in the case a rolling width is larger than the width of a slab to be rolled, a rolling in the transverse direction to the axis of the final rolling, i.e., a broadside rolling is effected to obtain a required rolling width, and thereafter, a rolling in the longitudinal direction, i.e., a final rolling to obtain a required rolling thickness.
However, at this time of broadside rolling, a difference in width between the opposite end portions and the center of the plate (hereinafter referred to as a "side crop") is produced, and it is known that this side crop is increased in proportion to the increase in a broadside rolling ratio (rolling width/material width) as shown in FIG. 1.
If the side crop as described above is increased, then problems such as misshaping and the like are caused to the plate after the rolling, thus causing a decrease in the yield.
Now, as the methods of decreasing the side crop as described above, heretofore, there have been proposed (1) a method wherein corners of opposite end portions of a plate are bulged out by effecting a rolling in the longitudinal direction (sizing pass) before a broadside rolling, and thereafter, a broadside rolling is effected in the transverse direction so as to decrease the side crops, (2) a method wherein roll crowns are formed into minus crowns, whereby the reduction at the central portions is decreased as compared with that at the opposite end portions of the plate after the broadside rolling, so as to decrease the side crops, and the like.
In the conventional method (1), if the reduction of the sizing pass is increased before the broadside rolling, then the side crop may be decreased, however, the reduction will be restricted. More specifically, the rolling width after the broadside rolling will be given by the following equation (1), thereby limiting the reduction of the sizing pass due to the length of roll barrel. EQU Rolling width after broadside rolling=Slab length.times.Slab thickness/(Slab thickness-reduction of the sizing pass)&lt;Length of roll barrel (1)
Furthermore, in the aforesaid conventional method (2), it is necessary to form the roll crowns into minus crowns in accordance with the side crop. On the other hand, since the side crop is varied according to the broadside rolling ratio, it is necessary to prepare rolls having various types of roll crowns. Futher, even if the rolls having various types of roll crowns are prepared, roll profiles are varied due to wear of rolls, so that it is very difficult to obtain proper side crops.